The diagnosis and treatment of many sleep-based disorders requires that the sleep of a patient be monitored using, for example, polysomnography (PSG). PSG is a comprehensive recording of the biophysiological changes that occur during sleep. PSG is a multi-parametric test that monitors many body functions, including brain, eye movements, muscle activity or skeletal muscle activation, heart rhythm, and breathing function or respiratory effort. Specifically, a patient's brain activity is monitored using electroencephalography (EEG), a measurement of electrical activity produced by the brain as recorded from electrodes placed on the scalp. Under current practice, at least four electrodes are placed near the central and occipital portions of the brain for obtaining EEG data. Additionally, a patient's eye movements are monitored using electrooculography (EOG), a measurement of electrical activity of the eyes as recorded from electrodes placed near both eyes. These electrodes provide a readout that can then be scored into different stages of sleep (e.g. wake, stage 1, stage 2, stage 3, stage 4, and rapid eye movement (REM)). A widely accepted method for scoring (i.e. assigning) different stages of sleep based on the presence of various graphoelements (e.g. SEM, BLINK, Spindle, K, Delta, Theta, and REM) is provided for in A Manual of Standardized Terminology, Techniques, and Scoring System for Sleep Stages of Human Subjects, edited by Allan Rechtschaffen and Anthony Kales (1968), commonly referred to as the R&K rules. The R&K rules prescribe an electrode setup consisting of four EEG channels and two EOG channels.
The complexity of many devices currently used in the field of sleep monitoring requires specialized training for their application and use. Currently, most sleep investigations must be performed in a laboratory environment. However, the diversity of sleep disorders and the specific nature of some of the treatments require recurrent investigations that are poorly suited for a laboratory environment due to both the cost and inconvenience to the patient. Moreover, monitoring the sleep of a patient in a laboratory environment may lead to error mainly because the patient has to sleep away from his or her bed during the investigation which affects the quality of sleep and potentially the diagnostic. While it would be desirable to migrate the sleep staging investigation from the specialized doctor's office to the home of the patient, attempts to implement unattended sleep staging have been hindered hitherto by the high failure rate of recordings due mainly to the patient's inappropriate application of electrodes because of lack of anatomical knowledge. Accordingly, there is a need for an improved method and system of sleep staging that is potentially suited for, but not limited to, unattended sleep diagnostic scenarios.